1. S URFACE G EOMETRY AND H EAT F LUX E FFECT ON T HIN W IRE N UCLEATE P OOL B OILING OF S UBCOOLED W ATER IN M ICROGRAVITY Troy Munro and Andrew Fassmann Mechanical and Aerospace Engineering Utah State University Heng Ban – Faculty Mentor 2011 AIAA Region VI Student Conference 1

2. N UCLEATE B OILING Characterized by presence of bubbles High heat transfer rates Governed by Newton’s law of cooling Wide range of terrestrial and possible space applications 2 2011 AIAA Region VI Student Conference Photo courtesy of Incropera Boiling regimes for water at 1 atm q” = h(T s – T ∞ ) q” - heat flux h – heat transfer coefficient T s – temperature of surface T ∞ – bulk temperature of fluid Pool Boiling

3. H EAT F LUX E FFECTS 3 2011 AIAA Region VI Student Conference CHF Nucleate boiling Film boiling Photos courtesy of Incropera

4. S URFACE G EOMETRY E FFECTS 4 2011 AIAA Region VI Student Conference Photo courtesy of Fukada Photo courtesy of Zhao Photo courtesy of Chyu

5. M ICROGRAVITY O BSERVATIONS 5 2011 AIAA Region VI Student Conference Photo courtesy of Fukada

6. O BJECTIVES Investigate the effects of surface geometry, heat flux, and gravity on nucleate boiling by observing: Onset of nucleate boiling characteristics Steady state heat transfer characteristics Bubble dynamics 6 2011 AIAA Region VI Student Conference

7. E XPERIMENTAL S ETUP 7 2011 AIAA Region VI Student Conference

8. T RANSIENT W IRE B EHAVIOR 8 2011 AIAA Region VI Student Conference

9. O NSET OF N UCLEATE B OILING 9 2011 AIAA Region VI Student Conference Steady condition before boiling Range of three wire onset heat flux Average wire temperature below saturation (Bubble dynamic effects on wire temperature)

10. E FFECTS OF S URFACE G EOMETRY 10 2011 AIAA Region VI Student Conference Single-wireThree-wireFour-wire Minimum Onset Heat Flux 825 kW/m 2 Between 396 and 519 kW/m 2 586 kW/m 2 Concentrated Surface Area to Total Surface Area 1:11:61:4

11. S TEADY S TATE H EAT T RANSFER 11 2011 AIAA Region VI Student Conference Efficiency of boiling heat transfer in 1g and 0g are similar More effective area (more active nucleation sites) in microgravity

12. B UBBLE D YNAMICS - J ETS 12 2011 AIAA Region VI Student Conference TC 1TC 2TC 3TC 4 Distance from wire 1 mm6 mm11 mm16 mm

13. R ELATIVE B UBBLE A REA A NALYSIS (RBAA) 13 2011 AIAA Region VI Student Conference

14. H EAT F LUX E FFECT - RBAA 14 2011 AIAA Region VI Student Conference

15. C ONCLUSIONS The unique twist of three-wires provides a surface geometry that reduces the required heat flux for onset boiling In many instances, steady state heat transfer is enhanced in microgravity in the range of 5-10% As heat flux increases, there is an increased tendency to form jets, which provide convective current normally absent in microgravity

16. A CKNOWLEDGEMENTS SpaceX Rocky Mountain NASA Space Grant Consortium USU College of Engineering USU Department of Physics USU Undergraduate Research Space Dynamics Lab American Aerospace Advisors National Instruments

17. Q UESTIONS

18. F UTURE R ESEARCH 18 2011 AIAA Region VI Student Conference Photo courtesy of Deng 1) Extend input power range up to critical heat flux (wire burnout) 2) Further resolve onset conditions for boiling 3) 2-D Heater: Electric pulses to ‘seed’ the bubbles Bubbles grow as they accept heat Possibility to control amount of cooling CHF

19. Geometry “Power Level” Input Current (A) Average Power (W) Average Heat Flux (kW/m 2 ) Single Wire 52.132.48599 62.373.11750 72.603.36786 82.814.401031 93.014.931168 Three-Wire 52.202.35397 62.463.17503 72.713.32559 82.914.41670 93.124.48777 Four-Wire 51.692.47512 61.913.04639 72.093.66689 82.264.44930 92.424.70992